Computer systems are expected to provide various entertainment features, such as high definition audio. High definition audio streams in a computer system are considered isochronous streams. By isochronous, it is meant that memory requests related to an input audio stream, or an output audio stream, should be serviced by the computer system within a specified latency time in order to provide a pleasing experience to the user. For example, if a request for an audio frame of data from memory is made, it should be serviced within some specified latency time period, for otherwise, there may be undesirable pauses in the output audio. Similarly, if an input audio stream originating from an microphone input is to be stored in the system memory of a computer system, then the frames of the input audio stream should be stored in system memory within some specified latency time period, for otherwise the input buffer may get overloaded and drop frames.
With the isochronous requirement to guarantee time-sensitive audio data delivery, the implementation of audio processing in prior art computer systems has been such that when the high definition audio stream is active, the DMI (Direct Media Interface) link between the audio controller and the memory controller is prohibited from entering into the so-called low power L1-state, and system memory DRAM (Dynamic Random Access Memory) does not enter into its C3-Self Refresh mode so as to be available for low latency accesses. But when the high definition audio stream is active, it would save power and be of utility if the DMI link could enter into the low power L1-state, and if system memory DRAM could enter into its C3-Self Refresh mode, without violating the isochronous requirement of the high definition audio stream.